It has heretofore been proposed in my U.S. Pat. No. 3,946,951 of Mar. 30, 1976, to process difficult to defiber stock in a vortical circulation pulper by reducing the clearance of the rotor/stator blades at the truncated conical attrition interface to zero and increasing the horsepower exerted on the zero clearance rotor at least fifty percent to achieve enough thrust and grinding action to refine the fibers.
The method operates successfully but subjects the rotor and stator to wear at a rapid rate. The rotor and stator can be made of wear resistant materials at increased cost, but economic factors make it desirable to find another solution to the problem.